1. Field of the Invention
The present invention relates to a differential capacitive type MEMS (Micro Electro Mechanical System) sensor apparatus provided with a capacitance compensator having a MEMS structure, and more particularly to a differential capacitive type MEMS sensor apparatus provided with a capacitance compensator having a MEMS structure, which comprises a MEMS structure including a differential capacitive type MEMS sensor and the capacitance compensator, so that the capacitances of the MEMS sensor are compensated for by the capacitance compensator in real time, is manufactured by a simple process, thus reducing production cost, and has a reduced size.
2. Description of the Related Art
Recently, various sensors have been used as essential elements according to the development of a micro multifunction system. The sensors include an inertia sensor, a hands tremble-compensating sensor, a heat-detecting sensor, an infrared ray sensor, etc. In addition, high performance sensors are developed vigorously so as to be used for specific purposes. Important research objectives of the sensors, which are currently under development, are “how they are micro-Miniaturized” and “how their electric power consumption rates are minimized”. Such objectives are achieved by a MEMS technique for manufacturing a three-dimensional movable structure by means of a semiconductor fabrication process. The structure includes a micro acceleration meter, a micro pressure gauge, etc. A MEMS (Micro Electro Mechanical System) denotes micro machinery used for electronic control and measurement purposes. That is, the MEMS is micro equipment, manufactured by a semiconductor fabrication process, which electronically operates and mechanically moves, thus differing from semiconductor devices. For example, one commonly used MEMS apparatus is an accelerometer of an air bag for a vehicle. The accelerometer has a micro size in order to sense fine variations in speed, and converts the movement of a speed meter located therein into voltage or current, thus determining whether or not the air bag should be operated. For this reason, the MEMS apparatuses have been applied to various micro sensors. Micro sensors using the MEMS technique are divided into capacitive type sensors and piezoelectric type sensors. Compared to the piezoelectric type sensors, the capacitive type sensors are advantageous in terms of ease of manufacture, heat characteristics, impact characteristics, operating frequency range, etc. However, the capacitive type sensors using the MEMS technique are disadvantageous in that capacitance thereof varies due to environmental changes such as temperature fluctuation, fine errors generated in a manufacturing process, and parasitic elements, without external input. Thus, the variation of the capacitance must be compensated for. One conventional method for compensating for the capacitance is described with reference to FIG. 1.
FIG. 1 is a circuit diagram illustrating the capacitance compensation of a conventional differential capacitive type MEMS sensor. When external physical force in a designated direction is applied to the conventional differential capacitive type MEMS sensor 110 shown in FIG. 1, capacitance exhibited between a movable structure and a fixed frame unit, located therein, is changed. The conventional differential capacitive type MEMS sensor 110 achieves a sensing function using the changed capacitance. In order to improve sensing capacity, the sensor 110 is a capacitive type, which comprises a differential structure and generates differential capacitances, such as a positive capacitance (+ΔC) and a negative capacitance (−ΔC), according to external force. The two capacitances are differentially amplified, thus allowing the sensitivity of the sensor 110 to be doubled.
Here, it is preferable that the positive and negative capacitances of the differential structure have the same value under the condition that external force is not applied to the sensor 110.
As described above, an error is generated between the differential capacitances, i.e., the positive and negative capacitances, due to various factors including a process error. In order to compensate for the error between the differential capacitances, the sensor 110 is connected to a capacitance compensating circuit 120 located outside, and capacities of variable capacitors C1 and C2 located in the capacitance compensating circuit 120 varies. Thereby, it is possible to compensate for the process error.
In the capacitance compensating circuit 120, a plurality of the variable capacitors C1 and C2 and a switching element for switching the connection of each of the variable capacitors C1 and C2 to the circuit 120 on/off. The switching of the switching element may be controlled by a digital signal of an external memory, or by means of a resistance element used for trimming.
Since the capacitances of the above-described conventional differential capacitive type MEMS sensor 110 are compensated for by means of a separately prepared circuit, the MEMS sensor 110 and the capacitance compensating circuit 120 must be respectively manufactured by additional processes. Further, since the capacitance compensating circuit 120 uses a plurality of the capacitors having a large size, the conventional differential capacitive type MEMS sensor 110 requires complicated designing and manufacturing processes, thus being increased in terms of size and production cost.